This invention relates to seismic equipment for acoustically investigating the earth structure and more particularly to acoustical borehole probe apparatus designed to acoustically investigate earth structure at a frequency of between 600 hz and 10 khz.
Most investigatory boreholes have a diameter between 50 and 100 mm. It is often desirable to accurately investigate the earth region within 75 feet of the borehole. Seismic equipment has been developed to perform a gross or macro-investigation utilizing frequencies below 500 hz. Additionally, borehole probe equipment has been developed for micro-investigating the earth structure along the borehole and radially a few feet from the borehole. However, it has been very difficult to develop equipment that is capable of micro-investigating the region from 5 feet to 75 feet from the 50 to 100 mm diameter borehole.
Acoustical probes have been developed utilizing piezoelectric transducers for emitting pulsed low level energy in the frequency of 500 hz to 10 khz into the surrounding earth structure. However, such low energy pulses are generally only effective between 5 to 10 feet from the borehole in high attenuating earth structures.
In recent years, acoustical sparker probe devices utilizing an electrical discharge between electrodes for generating high energy acoustical pulses have been developed. Such devices utilize a high capacity electrical energy storage bank near the borehole opening for generating an electrical discharge of greater than 100 joules between the probe electrodes. However the range or depth of the probe from the storage bank is greatly restricted. The energy transmission loss per unit of length from the storage bank to the probe electrode increases esponentially with the electrical current in the transmission line. Generally, such devices are limited to boreholes having depths of less than 40 meters. There is a substantial need for a high-energy acoustical probe apparatus capable of generating high energy acoustical pulses for investigating earth structure of up to 75 feet radially from the borehole at borehole depths of more than 40 meters.
One of the objects of this invention is to provide a sparker acoustical probe apparatus that is capable of developing high-energy, acoustical pulses in the 600 hz to 10 khz range at borehole depths considerably greater than 40 meters.
An additional object of this invention is to provide an acoustical sparker probe apparatus that is capable of storing high-voltage energy within the probe itself that is sufficient to generate acoustical, high-energy pulses.
A further object of this invention is to provide a new acoustical sparker probe apparatus in which the probe has a capability of generating high voltage electrical energy and storing the energy in the probe and discharging the energy between electrodes of a probe sparker system.
A still further object of this invention is to provide a sparker probe apparatus that is capable of generating and transmitting high energy acoustical pulses into the earth surrounding the borehole in which the high energy is stored within the borehole utilizing conventional electronic components.
An additional object of this invention is to provide an acoustical sparker probe apparatus that is capable of generating high energy acoustical pulses into the earth at depths considerably greater than 40 meters in which there is no decrease in the strength of the acoustical pulse as the probe moves further from the borehole opening.
A further object of this invention is to provide an acoustical sparker probe apparatus that is economical to manufacture and easy to operate.
An additional object of this invention is to provide an acoustical sparker probe apparatus having a high electrical energy storage capacity within a small diameter probe.
These and other objects and advantages of this invention will become apparent upon reading the following detailed description of a preferred embodiment.